Automatic compressor unloader



g- 1939- c; 6. EACH AUTOMATIC COMPRESSOR UNLdADER Filed May 21, 1938 INVENTOR.

Q 1 ll/ Patented Aug. 29, 1939 UNITED STATES PATENT OFFICE Vilter Manufacturing Company,

Milwaukee,

Wis., a corporation of Wisconsin Application May 21, 1938, Serial No. 209,201

12 Claims.

My present invention relates generally to improvements in the art of compressing fluids, and relates more specifically to improvements in the construction and operation of automatic unloadi'i ing devices for gas compressors or the like.

Generally defined, an object of my present invention is to provide an improved automatic unloader for compressors, which is simple in construction and efiicient in operation.

A more specific object of the invention is to provide an improved compressor unloader of the clearance pocket type and especially applicable to refrigerant gas compressors, which is extremely simple and compact in construction, and which is moreover rapid and reliablein operation.

While numerous types of so-called clearance pocket unloaders for refrigerant compressors, have heretofore been proposed, none of these prior devices have proven entirely satisfactory in commercial use, primarily because of their complicated structure and their failure to operate properly under varying conditions of operation of the compressors. These unloading mechanisms which are used in conjunction with various types of air and gas compressors, ordinarily include one or more clearance pockets which are communicable past automatically operable control valves, with the displacement chamber of the pump or compressor, so as to vary the capacity of the pressure pump in accordance with the demand for compressed fluid. The unloading valve or valves are ordinarily controlled either by means of thermostat located in the compressor suction line, or by an automatic pressure switch, or they may be controlled in any other suitable manner. It is necessary that the unloading valves be operable quickly and positively, if effective unloading is to be accomplished, and undue complications in these assemblages will necessarily detrimentally affect the accuracy and reliability of performance.

In accordance with my present improvement, I locate the clearance pocket of the unloading assemblage in the wall of the compressor cylinder and connect the same through a large valve controlled port directly with the delivery end of the displacement chamber, and through a small constantly open passage directly with the suction line. The control valve for the large port is operable to close the same by pump discharge pressure acting upon a valve actuating plunger, and to open the same by means of a simple spring coacting with the same plunger in opposition to the valve closing pressure. Release of the high valve actuating pressure is effected by means of a simple magnetically actuated by-pass valve controlled by a thermostat or by a pressure switch, and the entire system is so simple and foolproof in operation, that maximum efiiciency must necessarily result. The operation of my im- Y 5 proved unloading mechanism is also entirely automatic after proper initial adjustments have been made, and the device can be manufactured and installed at moderate cost and requires little attention.

A clear conception of an embodiment of the present invention, and of the mode of constructing and of operating automatic compressor unloaders built in accordance with the improve ment, may be had by referring to the drawing accompanying and forming a part of this specification wherein like reference characters designate the same or similar parts in the various views.

Fig. 1 is a fragmentary sectional view showing a portion of a compressor cylinder, piston and discharge valve mechanism, and also disclosing the internal structure of one of my improved clearance pocket unloaders and the connections associated therewith;

Fig. 2 is a transverse vertical section through the unloader, taken along the line 2-2 of Fig. 1 and drawn to a reduced scale; and

Fig. 3 is a section through the magnetically operated valve which is used in the unloader control system. 30

While I have shown an automatic compressor unloader which is especially applicable to a particular type of high pressure reciprocating singleacting compressor for handling refrigerant gases such as ammonia and freon, it is not the intent to thereby unnecessarily restrict the scope.

Referring to the drawing, the high pressure compressor shown therein is of relatively standard construction and comprises a cylinder 6 having a bore 1; a piston 8 reciprocable within the bore 1 and having one or more suction valves 9 associated directly therewith; and an end head I0 sealing the bore 1 and cooperating with the piston B to form a displacement chamber I I, the head It! being provided with one or more discharge valves I2 normally held to their seating by means of annular helical springs l3.

My improved automatic unloader which is as sociated directly with the gas compressor, comprises generally a clearance pocket H of any desired volume formed in the cylinder 6 and communicating through a small passage 15 with the compressor suction space; a relatively large port 16 connecting the pocket M with the displacement chamber l at the extreme end of the compression stroke of the piston 8; a main unloading valve ll for controlling the delivery of compressed gas to and from the chamber l and the pocket l3 through the port It, and having a stem ES to the outer end of which a valve actuating plunger l9 is rigidly attached; a casing 29 secured to the cylinder 5 and having therein a bore 2| with which the plunger I9 coacts and which is divided by this plunger into chambers 22, 23; a compression spring 24 disposed within the chamber 22 and coacting at its opposite ends with the casing 29 and with the plunger IS); a closure plate 25 for the chamber 23 and providing a support for an adjustable screw 26 for locking the valve l! in closed position; a magnetically operated pressure relief valve 21 automatically operable by a device 28 and being communicable through a pipe 29 with the chamber 23, and through another pipe 30 with the chamber 22 and with a suction connection 3|; and a high pressure inlet connection 32 communicating with the chamber 23. While the movement of the plunger l9 along the bore 2| is such that the piston may materally reduce the area of the port or connection 32 which admits high pressure gas to the chamber 23, this port should never be completely out oh, and the spring confining chamber '22 may also be provided with a small port 33 (shown in dot-and-dash lines in Fig. l) which con1municates with the suction line and which may be sealed by the plunger 59 when the unloading valve H is closed.

, The clearance pocket l4 may be formed directly in the cylinder 8 or in a separate casting, and there may be any desired number of these pockets and corresponding unloading mechanisms. The suction passage l5 should be relatively small, and may be omitted and replaced by venting clearance between the stem l8 and casing 26, and these vent passages are provided primarily for the purpose of preventing excessive pressure from building up in the pocket l4, and which would tend to keep the valve I! closed. The valve coacts with a bevel seat 34 and may be flexibly and detachably connected to the inner end of the stem l8 by means of a threaded collar 35 and ya spring 36 coacting with an enlarged end of the stem, so as to insure tight seating.

The casing 28 which-houses the plunger l9, may be removably attached to the cylinder 6 by means of studs 3?, and the closure plate 25 may be likewise attached to the casing 2!] by studs 38. A ring nut 39 serves to firmly attach the plunger IS to the stem |8,- and the plunger l9 is preferably of somewhat less diameter than the bore 2| and is provided with sealing rings All for throttling the port 32 and for preventing leakage of gas from the chamber 23 to the chamber 22. The adjustable screw 25 hasscrew thread coaction with the closure plate 25, at its inner end, and has its outer end provided with a polygonal actuating portion which is'normally confined and sealed within a detachable cap 3|. The locking screw 26 should also preferably be embracedby packing material 22 in order to prevent escape of high pressure gas 'therealong from the chamber 23 which, as previously stated, is in constant communication withthe high pressure discharge line of the compressor through the port or connection 32. The suction connection 3| may be omitted, but if provided, should be of restricted cross-section or should be variable in cross-section with the aid of a needle valve.

The automatic controlling device 28 may be either a thermostat operable by suction temperature, or a pressure switch, or any other type of apparatus for completing an electric circuit for actuating the magnetic valve 21. 21 may be of extremely simple and compact construction as shown in detail in Fig. 3, and comprises a casing having ports communicating with the pipes 29, 33 respectively, and also having a valve seat 43 therein; a valve plunger 44 normally held against the seat 43 by gravity and having an upper bar portion 45; and a coil 45 embracing the bar portion 45 and adapted to lift the valve plunger 44 against a stop 41 when the coil 46 is energized. The valve 21 may be located any desired distance from the device 28, and may even be built into the casing 20, and when the plunger 44 isvseated as in Fig. 3, high pressure gas is confined within the chamber 23, and the chamber 22 is open to suction through the pipes 30, 3|, thereby causing the unloading valve I! to remain closed as shown in the draw- During normal operation of the compressor, and when maximum discharge capacity is required, the unloading mechanism will not be functioning, as the valve I! will remain closed and the pocket through the passage l5, or past the stem l8 to the chamber 22. The high-pressure discharge pressure will be established and maintained in the chamber 23 through the connection 32, and the spring 24 will then be compressed within the chamber 22 which is also vented to suction through the pipes 30, 3|.

When the device 28 is actuated to energize the magnetic coil 46, as by reduction in load on the low pressure side of the compressor, the valve plunger 44 will be raised thus permitting high pressure gas to escape from the chamber 23 past the valve 2'! to the chamber 22 and to the suction line. This reduction or release of pressure in the chamber 23 causes the Spring 24 aided by the high discharge pressure in the chamber II, to become quickly effective to open the unloading valve l1 and to throttle the admission ofcfresh high pressure gas through the connection 32, and the opening of the valve permits some of the high pressure gas displaced by the reciprocating piston 8 to surge into and out of the pocket M as the piston approaches and recedes from the port l6. While a negligible quantity of the gas admitted to the pocket l4 during the compression stroke of the piston 8, escapes to the suction line through the restricted passage IE5 or past the valve stem !8 most of this gas is returned to the displacement chamber l| during the suction or return stroke of the piston; and if any high pressure gas is trapped within the pocket it due to sudden closing of the valve II, this gas will escape to the suction line through the passage 85, or past the stem 18 to the chamber 22. If the port 33 is used, this port will be uncovered when the plunger I9 is moved toward the screw 26 during opening of the valve l1, and will assist the suction pipe 3| in releasing pressure from within the chamber 22; but it maybe desirable to have the port 33 normally closed and the connection 3| so restricted, that gas under pressure released from the chamber 23 may act momentarily through the pipes 29, 30 to build up a slight gas This valve I M will be vented to suction pressure in the chamber 22 which will assist the spring 24 in opening the valve ll.

When the device 28 operates to break the electric circuit and to thereby deen rgize the coil 46, the valve plunger l4 drops and thus closes the valve 2"! thus cutting off the escape of gas from the chamber 23 through the pipe 29. High pressure gas then quickly fills the chamber 23 and acts upon the plunger iii in opposition to the spring 24 to close the unloading valve [1. In this manner, the unloading valve It will be quickly and posi tively opened and closed in response to the action of the controlling device 28, and when the Valve I1 is closed, the pressure in the pocket M will be quickly relieved, and the port 33 and pipe 3| will likewise quickly relieve the gas pressure from the chamber 22. The adjustable screw 28 may be readily adjusted to prevent opening movement of the valve H, and to also prevent complete closing of the port connection 32, by merely removing the cap 4| and by applying a wrench to the polygonal outer end of the stop 26; and the plate 25 and casing 28 may be conveniently removed to permit inspection of internal parts, by releasing the nuts coacting with the studs 38,391

From the foregoing detailed description it will be apparent that my present invention provides an extremely simple and compact automatically functioning unloading assemblage which is positive and reliable in action, and which may moreover be conveniently applied to standard air or other gas compressors. The extent of unloading will be dependent upon the periods for which the valve ll is retained open, and the length of these periods will be dependent upon the action of the control device 23. All portions of the improved assemblage, besides being extremely simple in structure, are conveniently accessible for inspection and adjustment, and the unloader has proven highly successful and satisactory in actual use. The venting of the clearance pocket M by means of a passage IE5 or otherwise, is relatively important, since this venting prevents accumulation of undesirably high gas pressure in the clearance pocket; and the throttling of the port connection 32 by the valve actuating plunger IS in order to prevent the high pressure gas from rushing into the chamber 23 when the valve 2'! opens, is also desirable. If this inrush of high pressure gases is not checked, the pressure in the chamber 23 will build up faster than it can be relieved by opening of the relatively small valve 21', and the spring 24 will be restrained from moving the plunger l9 to valve opening position. The magnetic valve 21 is also of extremely simple and compact construction, and all elements of the assemblage may obviously be manufactured, assembled and applied to a compressor system at moderate cost.

It should be understood that it is not desired to limit this invention to the exact details of construction, or to the precise mode of use herein shown and described, for various modifications within the scope of the claims may occur to persons skilled in the art.

I claim:

1. In combination with a compressor having suction and discharge valves and a piston displacement chamber communicable therewith, a clearance pocket communicable with the piston displacement chamber and. having constant restricted communication with the suction line, an unloading valve for controlling communication between said pocket and said chamber, and a plunger for operating said valve, said plunger being movable to close said valve by compressor discharge pressure and to open said valve by mechanical means.

2. In combination with a compressor having suction and discharge valves and a piston displacement chamber communicable therewith, a clearance pocket communicable with the piston displacement chamber at the end of the compression stroke of the piston and having a constantly open vent communicating with the compressor suction, an unloading valve for controlling communication between said pocket and said chamber, a plunger operable outside of said pocket for actuating said valve, means for subjecting said plunger to high fluid pressure to close said valve, and spring means for opening said valve when said high fluid pressure is released.

3. In combination with a compressor having suction and discharge valves and a piston displacement chamber communicable therewith, a clearance pocket communicable with the piston displacement chamber at the end of the piston compression stroke, an unloading valve for controlling communication between said pocket and said chamber, means forming an auxiliary chamber out of communication with said pocket and disposed in alinement with said valve, a valve actuating plunger movable in said auxiliary chainber, means for subjecting one side of said plunger to compressor discharge pressure andthe opposite side thereof to suction, and spring means for moving said plunger when the discharge pressure acting thereon is released.

4. A compressor unloader comprising, a clearance pocket communicable with the compressor displacement chamber and being constantly vented to the compressor suction. an unloading valve for controlling communication between said clearance pocket and the compressor displacement chamber, a plunger movable in one direction by compressor discharge pressure to close said valve and in the opposite direction by spring pressure and means operable by variations in compressor suction pressure for lay-passing high pressure fluid from one side of said plunger to the other.

5. A compressor unloader comprising, a clearance pocket communicable with the compressor displacement chamber at the end of the piston compressionv stroke, an unloading valve for controlling communication between. said pocket and said displacement chamber, and a plunger subjected to compressor discharge pressure to close said valve and to spring pressure to open said valve, said plunger being movable to throttle the admission of said discharge pressure when said valve is opened.

6. A compressor unloader comprising, a clearance pocket communicable with the compressor displacement chamber, an unloading valve for controlling communication between said pocket and said displacement chamber, a valve actuating plunger disposed outside of said pocket, a spring cooperable with said plunger to open said valve, and means for subjecting said plunger to compressor discharge pressure to close said valve.

'7. A compressor unloader comprising, a clearance pocket communicable with the compressor displacement chamber, an unloading valve for controlling communication between said pocket and said displacement chamber, a valve actuating plunger disposed outside of said pocket, a spring cooperable with said plunger to open said valve, means for subjecting said plunger to compressor discharge pressure to close said valve, and means for releasing pressure from said pocket to the compressor suction when said valve is closed.

8. A compressor unloader comprising, a clearance pocket communicable with the compressor displacement chamber, an unloading valve for controlling communication between said pocket and said displacement chamber, a valve actuating plunger disposed outside of said pocket, a spring cooperable with said plunger to open said valve, means for subjecting said plunger to compressor discharge pressure to close said valve, and a constantly open restricted vent for said pocket communicating with the compressor suction.

9. A compressor unloader comprising, a clearance pocket communicable with the compressor displacement chamber, an unloading valve for controlling communication between said pocket and said displacement chamber, a valve actuating plunger disposed outside of said pocket, a spring cooperable with said plunger to open said valve, and means for subjecting said plunger to compressor discharge pressure to close said valve, said plunger being movable to throttle the admission of compressor discharge pressure thereto when said valve is open.

10. A compressor unloader comprising, a clearance pocket communicable with the compressor displacement chamber at the end of the compression stroke, an unloading valve for controlling communication between said pocket and said displacement chamber, a plunger operable by com- ,pressor discharge pressure to close said valve, and

a magnetically operated valve operable by variations in compressor suction for controlling the valve closing pressure acting on said plunger.

11. A compressor unloader comprising, a clearance pocket communicable with the compressor displacement chamber at the end of the compression stroke, an unloading valve for controlling communication between said pocket and said displacement chamber, a plunger operable by compressor discharge pressure to close said valve, and a control valve operable by variations in suction load to by-pass fluid pressure from one side of said plunger to the other.

12. A compressor unloader comprising, a clearance pocket communicable with the compressor displacement chamber and being constantly restrictively vented to the compressor suction, an unloading valve for controlling communication between said pocket and said displacement chamber, a valve actuating plunger operable in an auxiliary chamber segregated from said pocket, means for admitting compressor discharge pressure to said auxiliary chamber on one side of said plunger, and a by-pass valve operable by variations in compressor suction to throttle the admission of compressor discharge pressure to said auxiliary chamber and to by-pass said pressure around said plunger.

CHARLES G. EACH. 

